Nervous Physio

• Functions of the Nervous System


  The master controlling and communicating system of the body
• Functions of the Nervous System

  • Sensory input: detects external and internal stimuli
  • Integration: processes and responds to sensory input
  • Control of Muscles and Glands
  • Homeostasis is maintained by regulating other systems
  • Center for Mental Activities
• Central Nervous System (CNS)


  Brain and spinal cord, encased in bone
• Peripheral Nervous System (PNS)


  Nervous tissue outside of the CNS, consists of sensory receptors and nerves
• Anatomical divisions of the Nervous System

  • CNS processes, integrates, stores, and responds to information from the PNS
  • PNS detects stimuli and transmits information to the CNS and receives information from the CNS
• Divisions of the PNS

  • Sensory division: transmits action potentials from sensory receptors to the CNS
  • Motor division: carries action potentials away from the CNS in cranial or spinal nerves
• Subdivisions of the Motor Division

  • Somatic nervous system: innervates skeletal muscle
  • Autonomic nervous system (ANS): innervates cardiac muscle, smooth muscle, and glands
• Subdivisions of the ANS


  • Sympathetic division: most active during physical activity (fight or flight)
  • Parasympathetic division: regulates resting functions (rest and digest)
  • Enteric nervous system: controls the digestive system
• Neurons


  Excitable cells that transmit electrical signals
• Non-neural cells (Glial cells)


  Cells that surround neurons, account for over half of the brain's weight
• Components of a Neuron

  • Cell body (soma): primary site of protein synthesis
  • Dendrites: short, branched cytoplasmic extensions that conduct electric signals toward the cell body
  • Axon: cytoplasmic extension that transmits action potentials to other cells
• Types of Neurons


  • Multipolar neurons: several dendrites and a single axon
  • Bipolar neurons: single axon and dendrite
  • Unipolar neurons: single axon
• Glial Cells of the CNS

  • Astrocytes
  • Microglial
  • Ependymal cells
  • Oligodendrocytes
• Glial Cells of the PNS

  • Satellite cells
  • Schwann cells
• Functions of Glial Cells


  • Provide supportive scaffolding for neurons
  • Segregate and insulate neurons
  • Guide young neurons to proper connections
  • Promote health and growth
• Astrocytes


  • Most abundant, versatile, and highly branched
  • Support and brace neurons and blood vessels
  • Anchor neurons to nutrient supplies
  • Influence the blood-brain barrier
  • Guide migration of young neurons
  • Process substances, recycle neurotransmitters
  • Isolate damaged tissue and limit inflammation
• Ependymal Cells


  • Line the ventricles of the brain and central canal of the spinal cord
  • Some specialized to produce cerebrospinal fluid
  • Help circulate cerebrospinal fluid using cilia
• Microglia


  • Small, ovoid cells with spiny processes
  • Phagocytes that monitor the health of neurons
• Oligodendrocytes


  • Form myelin sheaths around axons of several CNS neurons
• Schwann Cells


  • Form a myelin sheath around part of the axon of a PNS neuron
• Satellite Cells


  • Support and nourish neuron cell bodies within ganglia
• Myelinated Axons


  • Plasma membrane of Schwann cells or Oligodendrocytes repeatedly wraps around a segment of an axon to form the myelin sheath
  • Myelin functions to protect the axon, electrically insulate fibers, and increase the speed of nerve impulse transmission
  • Node of Ranvier - gaps in the myelin sheath
• Unmyelinated Axons


  • Rest in invaginations of Schwann cells (PNS) or Oligodendrocytes (CNS)
  • Conduct action potentials slowly
• White Matter


  Consists of myelinated axons, propagates action potentials, forms nerve tracts in the CNS and nerves in the PNS
• Gray Matter


  Collections of neuron cell bodies or unmyelinated axons, forms cortex and nuclei in the CNS and ganglia in the PNS, site of integration in the nervous system
• Action Potentials


  • Electric signals produced by cells
  • Can result in sensations of sight, hearing, and touch
  • Underlie complex mental activities like conscious thought, memory, and emotions
  • Cause contraction of muscles and secretion of glands
• CNS


  • Conducts action potentials slowly
• Fig. 10.10
• Gray matter


  Collections of neuron cell bodies or unmyelinated axons, forms cortex and nuclei in the CNS and ganglia in the PNS, axons synapse with neuron cell bodies which are functionally the site of integration in the nervous system
• Action potentials


  Electric signals produced by cells
• When action potentials are received from sensory cells


  It can result in the sensations of sight, hearing, and touch
• Complex mental activities, such as conscious thought, memory, and emotions

  Result from action potentials
• Contraction of muscles and the secretion of certain glands


  Occur in response to action potentials
• Ionic concentration differences across the plasma membrane

  Sodium ions (Na+), calcium ions (Ca2+), and chloride ions (Cl-) are in much greater concentration outside the cell than inside, Potassium ions (K+) and negatively charged molecules, such as proteins, are in much greater concentration inside the cell than outside, Negatively charged proteins are synthesized inside the cell and cannot diffuse out of it
• Na+-K+ pump


  Moves ions by active transport, potassium ions are moved into the cell, and Na+ are moved out of it
• Leak channels


  Always open, potassium ion leak channels are more numerous than Na+ leak channels, thus the plasma membrane is more permeable to K+ than to Na+ when at rest
• Gated ion channels


  Include ligand-gated ion channels, voltage-gated ion channels, and other gated ion channels
• Fig. 10.11
• Ligand-gated ion channels


  Open or close with the binding of a specific ligand (neurotransmitter), common in tissues such as nervous and muscle tissue, as well as glands
• Voltage-gated ion channels


  Open and close in response to small voltage changes across the plasma membrane, common in tissues such as nervous and muscle tissues